An amusement apparatus including a user-operated and controlled apparatus for self-infliction of repetitive blows to the user’s buttocks by a plurality of elongated arms bearing flexible extensions that rotate under the user’s control.

The machines are already in production, as Scientific American notes:

Smokey the hound dog, the mascot of the University of Tennessee, has deployed the butt kicker to taunt fans of rival Vanderbilt at a basketball game, beckoning them to descend from the stands for posterior stimulation. “It was lucky we won that game; otherwise we really would have been embarrassed,” Armstrong says. He has sold several machines for $600 to $800, including one to an amusement park in Blackpool, England, and another to a Christian fun park in North Carolina. The latter requested that labels on the machine that used the word “butt” be changed to “rear.”